Advanced CO2 Capture Process Using MEA Scrubbing: Configuration of a Split Flow and Phase Separation Heat Exchanger

AbstractCO2 capture process using aqueous Monoethanolamine (MEA) scrubbing is a well-proven and commercially-ready technology for reducing CO2 emission to the atmosphere. Although the MEA scrubbing is the one of the most suitable technologies for post-combustion CO2 capture, the MEA process has a critical problem which is high consumption of reboiler heat energy for solvent regeneration. In order to reduce the reboiler heat requirement, this paper suggests an advanced configuration of MEA process which consists of split flow and a phase separation heat exchanger. The split flow permits to reduce the reflux ratio in the stripper and the phase separation heat exchanger permits to alleviate preheating duty loss. As a result, the regeneration energy of the advanced process is reduced by 2.84GJ/ton CO2, which is lower than one of the reference process by 27%.CO2 capture; post combustion CO2 capture; advanced stripper configuration; cold solvent split; rich vapor compressio

Optimal Process Design of Onboard BOG Re-liquefaction System for LNG Carrier

High-pressure gas injection engines (HPGI) took center stage in LNG carrier propulsion systems after their advent. The HPGI engine system can be easily modified to include a re-liquefaction system by adding several devices, which can significantly increase the economic feasibility of the total system. This paper suggests the optimal operating conditions and capacity for a re-liquefaction system for an LNG carrier, which can minimize increases in the total annualized cost. The installation of a re-liquefaction system can save 0.23 million USD per year when the cost of LNG is 5 USD/Mscf. A sensitivity analysis with different LNG costs showed that the re-liquefaction system is profitable when the LNG cost is higher than 3.5 USD/Mscf

Simulation methodology for hydrogen liquefaction process design considering hydrogen characteristics

© 2022 Hydrogen Energy Publications LLCOne promising method to improve the storage capacity of hydrogen is to liquefy it, resulting in high energy density. However, liquefying hydrogen is a challenging task because hydrogen characteristics, such as a boiling point at a cryogenic temperature and changes in equilibrium compositions of spin isomers constituting hydrogen molecules, must be considered. For a design of a hydrogen liquefaction process, it is necessary to use an equation of state that can accurately calculate the properties of hydrogen, and to consider conversion reactions of the spin isomers. In this study, it is confirmed that the modified Benedict-Webb-Rubin equation is a suitable equation of state for simulating hydrogen liquefaction processes and that an equivalent model used in this study for the conversion reactions of the spin isomers shows reasonable results. Furthermore, the economic feasibility of the designed hydrogen liquefaction process is investigated based on energy optimization and economic analysis.N

Potential Explosion Risk Comparison between SMR and DMR Liquefaction Processes at Conceptual Design Stage of FLNG

An FLNG (floating liquefied natural gas) or LNG FPSO (floating production, storage and offloading) unit is a notable offshore unit with the increasing demand for LNG. The liquefaction process on an FLNG unit is the most important process because it determines the economic feasibility, but would be a hazard source because of the large quantity of hydrocarbons. While a high efficiency process such as C3MR has been preferred for onshore liquefaction processes, a relatively simple process such as the SMR (single mixed refrigerant) or DMR (dual mixed refrigerant) liquefaction process has been selected for offshore units because they require a more compact size, lighter weight, and higher safety due to their space limitation for facilities and long distance from shore. It is known that an SMR has the advantages of a simple configuration, small footprint, and lower risk. However, with an increased production rate, the inherent safety of SMR needs to be evaluated because of its small train capacity. In this study, the potential explosion risks of the SMR and DMR liquefaction processes were evaluated at the conceptual design stage. The results showed that an SMR has a lower overpressure than a DMR at the same frequency, only with a small production capacity of 0.9 MTPA. With increased capacity, the overpressure of the SMR was higher than that of the DMR. The increased number of trains increased the frequency in spite of the small amount of equipment per train. This showed that the inherent risk of an SMR is not always lower than that of a DMR, and an additional risk management strategy is recommended when an SMR is selected as the concept for an FLNG liquefaction process compared to the DMR liquefaction process

Process design and economic optimization of boil-off-gas re-liquefaction systems for LNG carriers

Recent LNG carriers are equipped with high pressure gas injection engines. However, there has been a lack of research on liquefaction processes for boil-off gas (BOG) on LNG ships driven by high pressure fuel. Thus, this paper investigates the economic feasibility of the additional BOG liquefaction facilities in the high pressure fuel supply system on the vessels. To utilize the existing BOG compressor for fuel production, the liquefaction was conducted by the Joule Thomson (JT) cycle, which can use the pressurized BOG as a working fluid. For the comparison of the fuel supply system and its variations with BOG liquefaction, they are optimized with respect to total annual cost (TAC) as the objective function. With an LNG price of 5 USD/MMBtu, the optimization results show that the use of BOG liquefiers on LNG vessels reduces the TAC by at least 9.4% compared to the high pressure fuel supply system. The use of a liquid turbine in the liquefaction configurations also resulted in 2.4% savings in TAC compared to the JT cycle based process. However, a sensitivity analysis with different LNG prices indicates that the liquefaction systems are not economical compared to the fuel supply system when the LNG price is lower than 4 USD/MMBtu

Novel propane-free mixed refrigerant integrated with nitrogen expansion natural gas liquefaction process for offshore units

The presence of propane inventory in offshore liquefaction processes increases the concerns for platform safety. To address this, we propose a novel liquefaction process that integrates propane-free mixed refrigerant and nitrogen expander cycles (MR-N-2). The proposed design adopts the advantages of both nitrogen expander and single mixed refrigerant (SMR) processes. The process was rigorously simulated using Aspen HYSYS, and the specific energy consumption was optimized as an objective function using the genetic algorithm technique. Additionally, the MR-N-2 process was investigated using exergy and sensitivity analyses to compare the obtained results with those of the previous studies. The results verify that both liquefaction and exergy efficiencies are improved by 27.15% and 14.92%, respectively, in comparison with those of the base case. Moreover, the MR-N-2 process exhibits enhanced energy efficiency compared to that of the various existing nitrogen expander-based processes. The energy savings of the proposed method varies between 3.2% and 61.7%, and the cycle capacity is 22.43% better than that of the SMR process. (C) 2021 Elsevier Ltd. All rights reserved.N

Life cycle cost analysis of CO2 compression processes coupled with a cryogenic distillation unit for purifying high-CO2 natural gas

Novel compression processes coupled with a cryogenic distillation unit are designed in this study to puri fy high-CO2 natural gas or biogas before injection into the reservoir. Four different designs are evaluated to achieve the required injection pressure and minimize both the capital and operation costs. Depending on the pressure-temperature pathway for the compression of the top and bottom products of the distillation unit, the energy and equipment costs are quantified using process simulation models and economic analysis tools, which are integrated with the flow simulation model to determine the required injection pressure. This holistic approach of integrating the compression process and injection pipeline is efficient for optimizing the process design and operation variables. The results suggest that liquefying the top product followed by mixing with the bottom product is the most cost-effective method, as it eliminates costly compressors and simplifies the process configuration. In addition to the li f e cycle cost analysis of the process, the sudden release of CO2 from the vessel is also studied experimentally. The results show that releasing gaseous CO(2)through the valve induces the formation of solid CO2 inside the vessel before complete removal of CO2 from the vessel, thus requiring a controlled release strategy to avoid solid CO2 formation inside the vessel and through the valve.N

Process design of onboard membrane carbon capture and liquefaction systems for LNG-fueled ships

This study proposes an onboard membrane carbon capture and liquefaction system for LNG-fueled ships to satisfy the IMO's 2050 greenhouse gas reduction targets. The exhaust gas from a natural gas ship has a low CO2 fraction (similar to 3%) and high O-2 fraction (similar to 16%) compared to the flue gas from power plants. Herein, considering the above distinguishing features, a membrane carbon capture and liquefaction system has been proposed that is energy efficient and compact for the application of ships. To ascertain the performance of the proposed membrane-based system, it is compared to an amine-based onboard system in terms of energy consumption and major equipment size. This work evaluates four process configurations by varying the number of membrane stages and associated liquefaction processes at different CO2/N-2 selectivity and CO2 permeance. The results show that energy consumption (3.98 GJ(e)/t(LCO2)) is higher than the amine-based system (3.07 GJ(e)/t(LCO2)) at the CO2/N-2 selectivity of 50, but it can be decreased to 3.14 and 2.82 (GJ(e)/t(LCO2)) with an improved selectivity of 100 and 150, respectively. The major equipment size decreases to 54%, 28%, and 20% of the amine-based system when the permeance is 1000, 2000, and 3000 GPU, respectively. The results indicate that the new onboard membrane carbon capture and liquefaction system can be a competitive solution for the IMO's greenhouse gas reduction targets for 2050.N